Combinatorial design, selection and synthesis of peptide inhibitors against human glutathione transferase p1-1

Certain glutathione S-transferase (GST) isoenzymes detoxify the cell from xenobiotics, thus becoming inhibition targets when overexpressed in various tumours leading to MDR. We developed a combinatorial strategy aiming at designing peptide inhibitors against the hGSTP1-1 isoenzyme involved in MDR. We employed a combinatorial peptide library featuring engineered E. coli cells harboring a plasmid able to express a fusion protein containing random 12 peptides which were inserted into the active loop of thioredoxin, which itself was inserted into the dispensable region of the flagellin gene. After five selection rounds, clones were screened for hGSTP1-1 binding and those with the strongest signal were selected and sequenced. Sequence alignments showed a core binding sequence which, along with selected peptide fragments, were synthesized using the solid phase methodology and Fmoc/tBu chemistry on 2-chlorotrityl chloride solid support. The four peptides were studied for their inhibition potency against hGSTP1-1 allozymes A, B and C

Isoenzyme- and Allozyme-Specific Inhibitors: 2,20-Dihydroxybenzophenones and Their Carbonyl N-Analogues that Discriminate between Human Glutathione Transferase A1-1 and P1-1 Allozymes

The selectivity of certain benzophenones and their carbonyl N-analogues was investigated towards the human GSTP1-1 allozymes A, B and C involved in MDR. The allozymes were purified from extracts derived from E. coli harbouring the plasmids pEXP5-CT/TOPO-TAhGSTP1* A, pOXO4-hGSTP1*B or pOXO4-hGSTP1*C. Compound screening with each allozyme activity indicated three compounds with appreciable inhibitory potencies, 12 and 13 with P1-1A 62% and 67%, 11 and 12 with P1-1C 51% and 70%, whereas that of 15 fell behind with P1-1B (41%). These findings were confirmed by IC50 values (74–125 lM). Enzyme inhibition kinetics, aided by molecular modelling and docking, revealed that there is competition with the substrate CDNB for the same binding site on the allozyme (Ki(13/ A) = 63.6 +- 3.0 lM, K (15/B) = 198.6 +- 14.3 lM, and Ki(11/ C) = 16.5 +- 2.7 lM). These data were brought into context by an in silico structural comparative analysis of the targeted proteins. Although the screened compounds showed moderate inhibitory potency against hGSTP1-1, remarkably, some of them demonstrated absolute isoenzyme and/or allozyme selectivity

Peptide cell-display for selection of inhibitors against human glutathione transferase P1-1 (hGSTP1-1) allozymes

We developed a combinatorial strategy aiming at designing peptide inhibitors against the hGSTP1-1 isoenzyme involved in MDR. We developed a combinatorial strategy aiming at designing peptide inhibitors against the hGSTP1-1 isoenzyme. We employed a combinatorial peptide library featuring engineered E. coli cells harboring a plasmid able to express a fusion protein containing random 12peptides. After five selection rounds, clones were screened for hGSTP1-1 binding (dot blot hybridization) and those with the strongest signal were selected and sequenced. Sequence alignments showed a core binding sequence which, along with selected peptide fragments, were synthesized using the solid phase methodology . The synthetic peptides were studied for their inhibition potency against three human GSTP1-1 allozymes, A, B and

The Interaction of the Chemotherapeutic Drug Chlorambucil with Human Glutathione Transferase A1-1: Kinetic and Structural Analysis

Glutathione transferases (GSTs) are enzymes that contribute to cellular detoxification by catalysing the nucleophilic attack of glutathione (GSH) on the electrophilic centre of a number of xenobiotic compounds, including several chemotherapeutic drugs. In the present work we investigated the interaction of the chemotherapeutic drug chlorambucil (CBL) with human GSTA1-1 (hGSTA1-1) using kinetic analysis, protein crystallography and molecular dynamics. In the presence of GSH, CBL behaves as an efficient substrate for hGSTA1-1. The rate-limiting step of the catalytic reaction between CBL and GSH is viscosity-dependent and kinetic data suggest that product release is rate-limiting. The crystal structure of the hGSTA1-1/ CBL-GSH complex was solved at 2.1 A° resolution by molecular replacement. CBL is bound at the H-site attached to the thiol group of GSH, is partially ordered and exposed to the solvent, making specific interactions with the enzyme. Molecular dynamics simulations based on the crystal structure indicated high mobility of the CBL moiety and stabilization of the Cterminal helix due to the presence of the adduct. In the absence of GSH, CBL is shown to be an alkylating irreversible inhibitor for hGSTA1-1. Inactivation of the enzyme by CBL followed a biphasic pseudo-first-order saturation kinetics with approximately 1 mol of CBL per mol of dimeric enzyme being incorporated. Structural analysis suggested that the modifying residue is Cys112 which is located at the entrance of the H-site. The results are indicative of a structural communication between the subunits on the basis of mutually exclusive modification of Cys112, indicating that the two enzyme active sites are presumably coordinated

In silico design of 2,2'-dihydroxybenzophenones and xanthone analogues to inhibit human glutathione transferase's (hGSTs) involvement in Multiple Drug Resistance.

Glutathione S-transferases catalyze the conjugation of glutathione (GSH) to a variety of hydrophobic substrates, rendering them hydrophilic and facilitating their metabolic processing and secretion from the cell. GSTs are involved in major detoxification mechanisms of the cell from several xenobiotics and drugs. On the other hand, on the basis of the same detoxification mechanisms, cancer cells may acquire resistance by overexpressing GST activities, thus hampering the effectiveness of certain chemotherapeutic drugs and leading to chemotherapeutic resistant tumor cells. Several synthetic drugs and prodrugs exhibiting inhibition potency against GSTs have been proposed as strategies to overcoming multiple drug resistance (MDR) attributed to GST overexpression. In the pursuit of identifying new lead compounds as inhibitors against hGSTs involved in MDR we have used Structure Based Ligand Design techniques to generate in silico xanthone and benzophenone derivatives and performed extensive molecular docking and binding evaluation on the structure of hGSTA1-1

Synthesis of glutathione analogues and screening as substrates & inhibitors for human glutathione transferase p1‐1

A major detoxification mechanism of the cell involves the glutathione transferase (GST)‐catalyzed formation of glutathione (GSH) conjugates with various xenobiotics Based on the same mechanism, GST overexpression may lead to multidrug resistant phenotypes Therefore, several compounds with inhibitory potency against GSTs have been developed as potential tools fortackling GST-­‐attributed MDR. Several individual compounds and prodrugs have been proposed as GST‐inhibiting substances. In addition, GSH analogues have been considered as specific GST inhibitors, with particular attention been directed towards the synthesis of GSH analogues stable against γ‐glutamyltranspeptidase (γGT) and peptidases, as GST inhibitors

Synthesis and Study of 2‑(Pyrrolesulfonylmethyl)‑N‑arylimines: A New Class of Inhibitors for Human Glutathione Transferase A1‑1

Overexpression of human GSTA1-1 in tumor cells is part of MDR mechanisms. We report on the synthesis of 11 pyrrole derivatives as hGSTA1-1 inhibitors starting from 1-methyl-2-[(2-nitrobenzylsulfanyl]-1H-pyrrole. Molecular modeling revealed two locations in the enzyme H binding site: the catalytic primary one accommodating shorter and longer derivatives and the secondary one, where shorter derivatives can occupy. Derivative 9, displaying the highest inhibition and bearing a p-nitroarylimino moiety, and derivative 4, lacking this moiety, were studied kinetically. Derivative 9 binds (Ki(9) = 71 ± 4 μM) at the primary site competitively vs CDNB. Derivative 4 binds (Ki(4) = 135 ± 27 μM) at the primary and secondary sites, allowing the binding of a second molecule (4 or CDNB) leading to formation of unreactive and reactive complexes, respectively. The arylmethylsulfonylpyrrole core structure is a new pharmacophore for hGSTA1-1, whereas its derivative 9 may serve as a lead structure

2,20-Dihydroxybenzophenones and their carbonyl N-analogues as inhibitor scaffolds for MDR-involved human glutathione transferase isoenzyme A1-1

The MDR-involved human GSTA1-1, an important isoenzyme overexpressed in several tumors leading to chemotherapeutic-resistant tumour cells, has been targeted by 2,2′-dihydroxybenzophenones and some of their carbonyl N-analogues, as its potential inhibitors. A structure-based library of the latter was built-up by a nucleophilic cleavage of suitably substituted xanthones to 2,2′-dihydroxy-benzophenones (5–9) and subsequent formation of their N-derivatives (oximes 11–13 and N-acyl hydrazones 14–16). Screening against hGSTA1-1 led to benzophenones 6 and 8, and hydrazones 14 and 16, having the highest inhibition potency (IC50 values in the range 0.18 ± 0.02 to 1.77 ± 0.10 μM). Enzyme inhibition kinetics, molecular modeling and docking studies showed that they interact primarily at the CDNB-binding catalytic site of the enzyme. In addition, the results from cytotoxicity studies with human colon adenocarcinoma cells showed low LC50 values for benzophenone 6 and its N-acyl hydrazone analogue 14 (31.4 ± 0.4 μM and 87 ± 1.9 μM, respectively), in addition to the strong enzyme inhibition profile (IC50(6) = 1,77 ± 0.10 μM; IC50(14) = 0.33 ± 0.05 μM). These structures may serve as leads for the design of new potent mono- and bi-functional inhibitors and pro-drugs against human GTSs